Battery remaining time may be calculated in a main controller in a conventional manner in accordance with the charge remaining in the battery and with measured current loading information. It may be desirable to reduce the total current loading from the battery relative to that in normal operation in order to lengthen the battery remaining time, during battery backup operation. Accordingly, a system or main controller may control which device/function should remain energized and which should be powered down or disabled during battery backup operation.
Also, a function/device may self-monitor calculated data that is indicative of battery remaining time and initiate its own shutdown when the data indicates that the battery remaining time is below a threshold value.
Assume that a self-monitoring function/device “A” is required to remain operational, during battery backup operation; whereas, a function/device “′B” is required to go into shutdown in order to lengthen the battery remaining time in a manner to enable self-monitoring function/device “A” to remain operational for a longer time. It was discovered that such arrangement potentially could, disadvantageously, create a “race” condition. For example, if the required shutdown of function/device “′B” were to be delayed immediately following the interruption, the measured excessive instantaneous current loading could cause the battery remaining time indicative data to be temporarily indicative of a value that is lower than the threshold value associated with self-monitoring function/device “A”. This might cause a “race” resulting in self-monitoring function/device “A”, undesirably, going into shutdown. It may be desirable to avoid such “race” condition.
In carrying out an inventive feature, during an interval having a length of, for example, 4 minutes, that follows a change from normal operation to battery backup operation, the battery remaining time is calculated in a manner that is affected less or not at all by the measured instantaneous current loading.